Houda Sassi-Chamsi

Composition of the Jury

Abstract

According to INCa, 40% of cancers and chronic diseases are preventable, as they are linked to our lifestyles (smoking, an unbalanced diet, alcohol, and lack of physical activity). In light of this alarming figure, the best approach is prevention, particularly through persuasive communication. Motivation is a key element of the theories and models used in the field of persuasive communication. While these theories and models have emphasized the intensity of motivation, in this dissertation we propose an alternative theoretical framework: Ryan and Deci’s (1985, 2000) Self-Determination Theory (SDT), which instead considers the type of motivation (controlled vs. autonomous) in explaining behavioral change through the satisfaction (versus frustration) of fundamental psychological needs (autonomy, competence, and relatedness). This thesis aims to identify the characteristics of persuasive messages likely to motivate target populations to change their harmful behaviors (Study 1: quitting smoking) and adopt healthy behaviors (Study 2: increasing daily physical activity) with a view to preventing the onset of chronic diseases, based on SDT. The moderating role of social distance (Levels of Representation Theory) was examined through the characteristics of social networks (Facebook, Instagram, and Twitter). To conduct this research effectively, two experiments were carried out in which the delivery characteristics of the persuasive messages were manipulated. In the first experiment, conducted with 203 young smokers aged 18 to 34, the independent variable—message tone (supportive versus prescriptive)—and the moderator variable—social distance (proximal versus distal)—were manipulated. In the second study, conducted with 298 young adults also aged 18 to 34, a second independent variable was manipulated: the nature of the goals (intrinsic versus extrinsic). In general, the results show that a persuasive message with a supportive tone is more effective when conveyed by a source distant from the target (public health agency, Twitter), and that a persuasive message with a prescriptive tone is more effective when conveyed by a source close to the target (friends, Instagram). These combinations foster autonomous motivation through the satisfaction of fundamental psychological needs. This dissertation complements existing research by proposing an alternative theoretical framework that emphasizes the type of motivation and incorporates social distance as a moderating variable. It is the first to show that a prescriptive tone can generate a high level of behavioral intention, provided that the entity conveying the message is socially distant. The results are discussed, and future research directions are outlined, some of which address the limitations of our study.

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